The Control Effect Of Electrostatic Interaction On The Adsorption Of Ionic Organic Pollutants

Carbon based adsorption material is a new kind of engineering material, and it has been pouring into vision of people. Due to the unique physical and chemical properties, it has been widely used in industry. Because of its perfect structure and clear surface, it is a good model to study the adsorption mechanism of pollutant. Ionic compounds whose Kow is smaller have large solubility in water. The strong mobility of ionic compounds may bring greater risks to the ecological environment and human health. But because of the change of the molecular shape with pH value, the adsorption characteristics of different forms of pollutants may be different. And it had became a bottleneck to understand their apparent adsorption behavior. When the ionic contaminants into the environment, adsorption on soil and sediments plays an important role in controlling their environmental behavior. Therefore, it is helpful to explain the trend of ionic organic pollutants and carbon based adsorption materials to the environment, and that can evaluate significantly their the ecological riskIn the first study, the effects of sulfamethoxazole (SMX) on adsorption of phosphorus by carbon nanotubes (CNTs) were investigated at different pH. The adsorption of phosphorus by CNTs was significantly pH-dependent as indentified by the higher adsorption at low pH but lower adsorption at high pH. The electrostatic interactions should be the dominant mechanism. The adsorption of phosphorus on CNTs decreased due to the competition of SMX. The competitive adsorption was also pH-dependent. The changed species of phosphorus and SMX with changing pH led to changed interaction between phosphorus and CNTs due to electrostatic neutralization or repulsion.In the second study, as the graphene oxide (GO) and graphite (GP) were the model adsorbents, and the adsorption mechanism of benzoic acid, o-chlorobenzoic acid and p-chlorobenzoic acid on GO and GP were investigated at different pH. The contribution of different forms of pollutants to their apparent adsorption was quantified. But also the dominant adsorption mechanism of different forms of pollutants was determined. The results showed that the adsorption behavior was influenced by pH which can change the ionic contaminants form. The neutral molecules of benzoic acid and chlorinated derivatives were adsorbed through the hydrophobic interaction with carbon based materials and the adsorption of ionic contaminants inhibited significantly by electrostatic repulsion.